This application claims the benefit of Japanese Patent application No. 2001-050526 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an episcopic illumination device for a microscope and particularly to an episcopic fluorescent illumination device suitable for fluorescent illumination. The present invention relates to a microscope equipped with the episcopic illumination device.
2. Related Background Art
In general, the Koehler illumination method is utilized for episcopic illumination of a microscope. The Koehler illumination method is the one in which an image of a light source is projected to a pupil surface of an objective lens and the objective lens serves also as the role of a condenser lens to illuminate a specimen.
A light source magnification is an important factor for determining the brightness of illumination and the uniformity of illumination in the Koehler illumination method. Here, the light source magnification means a projection magnification that is the ratio of the size of the light source image formed in the vicinity of the pupil surface of the objective lens to the size of the light source.
In order to increase the brightness of illumination, it is necessary to increase the light source magnification. On the other hand, in order to improve the uniformity of illumination, it is necessary to decrease the light source magnification. Therefore, the brightness of illumination and the uniformity of illumination are in the relationship of trade-off with respect to the light source magnification.
The Koehler illumination method and the light source magnification will be described hereinafter by reference to FIGS. 5A and 5B. FIGS. 5A and 5B are diagrams showing the concept of the Koehler illumination method. FIG. 5A is the diagram showing a light beam illuminating the center of a specimen. FIG. 5B is the diagram showing a light beam illuminating the outermost periphery of the specimen.
First, the structure of the illumination system in FIGS. 5A and 5B will be described.
Light emitted from a light source 1 is projected on a pupil surface 9 of an objective lens 10 via a collector lens 2 (focal distance: f2) and a light source image forming lens 3 (focal distance: f3). At this time, the light source magnification xcex2 is xcex2=f3/f2. The projected light illuminates a specimen 11 (the diameter of the illuminated area: "PHgr"11) with the objective lens 10 (focal distance: f10) as a condenser lens.
Next, the relationship between the light source magnification and the brightness of illumination will be described with reference to FIG. 5A.
From FIG. 5A, when the light source 1 is a circular surface light source, the diameter of the image of the light source 1 projected on the pupil surface 9 of the object lens 10 is expressed as the following equation:
S9=xcex2xc3x97S1xe2x80x83xe2x80x83(1)
wherein
S1: the diameter of the light source when the light source is the circular surface light source,
S9: the diameter of the light source image projected on the pupil surface of the objective lens, and
xcex2: the light source magnification.
Therefore, the numerical aperture NA10 of the illumination light illuminating the specimen 11 is expressed as the following equation:                                                         NA10              =                              S9                /                                  (                                      2                    xc3x97                    f10                                    )                                                                                                        =                                                (                                      β                    xc3x97                    S1                                    )                                /                                  (                                      2                    xc3x97                    f10                                    )                                                                                        (        2        )            
wherein
NA10: the numerical aperture of the illumination light, and
f10: the focal distance of the objective lens 10.
The brightness of illumination is proportional to the square of the numerical aperture NA10. Therefore, from the equation (2), the brightness of the Koehler illumination is proportional to the square of the light source magnification xcex2. Accordingly, in order to increase the brightness of illumination, it is necessary to increase the light source magnification.
Next, the relationship between the light source magnification and the uniformity of illumination will be described with reference to FIG. 5B.
From FIG. 5B, the beam illuminating the periphery of the specimen 11 has an angle xcex81 with respect to an optical axis AX when emitted from the light source 1. Here, the relationship between the angle xcex81 and the diameter "PHgr"11 of the illuminated area of the specimen 11 is obtained. Assuming that the entire optical system satisfies the sine condition, the numerical aperture on an aperture diaphragm AS is expressed by the following equation:
NA9="PHgr"11/(2xc3x97f10)xe2x80x83xe2x80x83(4)
wherein
NA9: the numerical aperture on the aperture diaphragm AS, and
"PHgr"11: the diameter of the illuminated area of the specimen 11.
The numerical aperture when the beam from the light source 1 is incident on the collector lens 2 is the sine of the angle xcex81, and from the equation (4), is expressed by the following equation:                                                                         SIN                ⁢                                  xe2x80x83                                ⁢                                  θ                  ⁢                  1                                            =                              NA                ⁢                                  xe2x80x83                                ⁢                1                                                                                        =                              β                xc3x97                NA9                                                                                        =                                                (                                      β                    xc3x97                                          Φ                      ⁢                      11                                                        )                                /                                  (                                      2                    xc3x97                    f10                                    )                                                                                        (        3        )            
wherein
NA1: the numerical aperture when the beam from the light source is incident on the collector lens 2, and
SIN xcex81: the sine of the angle formed between the beam from the light source 1 for illuminating the periphery of the specimen 11 at the time of the emission and the optical axis.
From the equation (5), the SIN xcex81 of the angle xcex81 is proportional to the light source magnification xcex2. In general, the intensity of the light emission from the light source 1 is decreased as the angle xcex81 is increased. The decrease of the intensity of the light emission causes limb darkening of the illumination, deteriorating the uniformity of the illumination. Accordingly, in order to improve the uniformity of the illumination while reducing limb darkening, it is necessary to decrease the light source magnification xcex2 to reduce the angle xcex81.
As above, at the time of designing an illumination system, it is necessary to balance the brightness of illumination with the uniformity of illumination. Therefore, taking into consideration a light source to be used, a pupil diameter of an objective lens and an image surface size, an optimum light source magnification is set.
Due to the spread of high sensitivity cameras in recent years, it has become possible to observe things that could not be watched for the sake of darkness previously. Therefore, the scope of observable objects has been widened. Accordingly, a form of observation has been shifted from that with the aid of naked eyes in close contact to that with the aid of TV camera (TV observation).
Consequently, it is necessary to optimize the light source magnification of an episcopic illumination device not only for an image surface size of an eyepiece portion but also for that of a TV camera. The image surface size of the TV camera is small as compared with that of the eyepiece portion. Therefore, for TV observation, the illumination device is required to increase the brightness of illumination while maintaining the uniformity of illumination. Then, in order to increase the brightness of illumination, it is necessary to increase the light source magnification, as mentioned above.
As a method for optimizing a light source magnification even for an image surface size of a TV camera, there is a known method wherein a zoom variable power optical system is utilized in an illumination optical system to vary the light source magnification successively. As a concrete example of the illumination optical system with the zoom variable power optical system, there is an illumination optical system disclosed in the Japanese Patent Laid-Open Publication No. 2-16517. The illumination optical system is a Koehler illumination system by the use of an afocal zoom variable power optical system. However, in this system, it is necessary to form a collector lens with a telecentric optical system on the side of the light emission. In this case, the whole illumination optical system becomes complicated.
The present invention is made in view of the above problems, and it is an object of the present invention to provide a microscope episcopic illumination device and a microscope having simple structure, having an aperture diaphragm and a field stop, and being capable of setting an optimum light source magnification in accordance with change of an image surface size required for from eyepiece observation to TV observation.
The above object is achieved by providing a microscope episcopic illumination device having a light source for supplying light, a collector lens system for converting the light from the light source into parallel light flux, an aperture diaphragm, a light source image forming lens system for forming an image of the light source in the vicinity of the aperture diaphragm, a pupil relay lens system for re-forming the image of the light source formed in the vicinity of the aperture diaphragm in the vicinity of a pupil surface of an object lens system, and a field stop provided between the aperture diaphragm and the pupil surface of the object lens system, wherein the light source image forming lens system is a lens system with a variable finite focal distance, and varies a projection magnification of a ratio of the size of the re-formed image of the light source in the vicinity of the pupil surface of the object lens system to the size of the light source by changing the focal distance thereof.
A microscope of the present invention is characterized by having: the microscope episcopic illumination device according to the present invention; at least a camera port for mounting an electronic camera; a light path switching member for switching a light path of light from a specimen in order to direct the light from the specimen either to said camera port or to an eyepiece portion; a drive unit for varying the focal distance of the light source image forming lens system; and a controller for controlling the drive unit, wherein the controller controls the drive unit to set the projection magnification based on the size of an image pick-up surface of the electronic camera mounted on the camera port.